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1.0 METHODOLOGIES AND ASSUMPTIONS <br />1.1 SEDCAD+ HYDROLOGIC COMPUTER MODEL <br />Calculations for all ponds channels and culverts were performed utilizing the SEDCAD+ or <br />SEDCAD4 computer model developed by Civil Software Design. SEDCAD will be used in the <br />following discussion to represent both SECAD+ and SEDCAD4. SEDCAD is a hydrologic, <br />hydraulic, and sediment calculation model designed for use on computer systems. The SEDCAD <br />hydrologic model calculates runoff volume and peak flow via a numerical modeling techtuque based <br />on user inputs of a design storm event, (i.e., preupitation frequency data, selection of rainfall <br />distribution, and convolution increment). Hydrographs are developed on asub-watershed basis with <br />the input of area, tune of concentration, SCS curve number, and the selection of a hydrograph shape. <br />Routing of hydrographs is accomplished by the bfuskingum Method. <br />Inputs to the hydrology component of the SEDCAD computer model include: <br />• Precipitation Distribution <br />• S[Oftn Duranon <br />• Renrrn Period/Precipitation <br />• Hydrograph Response Shape <br />• Drainage Basin Area <br />• Time of Concentration <br />• Muskingum Routing Parameters <br />• Curve Number <br />Input values used in this model, are shown on the SEDCAD printouts and are explained in the <br />following text. <br />Precipitation Distribution <br />A predpitauon distribution is input to model the runoff hydrograph. SEDCAD allows the user to choose <br />between the SCS Type I and Type ]I Stomrs. The SCS Type I7 Storm was used Eor the Somerset Sanborn <br />• Creek, and Elk Creek Tvline areas. <br />